...They live a grim existence — a routine of trying to eat, to stay warm and dry, to gather firewood and water out in the elements, all while listening for the sounds of incoming planes and artillery shells.

Explanations of the origins of these underground shelters, many of which are set among other Roman ruins, vary from squatter to squatter. Some say they once were pens for livestock. Others say they were temporary quarters, occupied while more impressive dwellings were built in the centuries before Jesus. Perhaps some were crypts.

Whatever the intention of those who first dug them, Syria’s caves have become essential once more, restored to modern use because their thick walls offer a chance of survival to a population under fire....